text: #include "jpeglib.h"
  #include <setjmp.h>
  
  
  static unsigned char* put_scanline_someplace(unsigned char *currPtr,JSAMPLE *buffer, int row_stride) {
    memcpy((void*)currPtr,(void*)buffer,row_stride);
    return currPtr+row_stride;
  }
  
  struct my_error_mgr {
    struct jpeg_error_mgr pub;    /* "public" fields */
    jmp_buf setjmp_buffer;        /* for return to caller */
  };
  
  typedef struct my_error_mgr * my_error_ptr;
  
  void my_error_exit (j_common_ptr cinfo) {
    /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
    my_error_ptr myerr = (my_error_ptr) cinfo->err;
  
    /* Always display the message. */
    /* We could postpone this until after returning, if we chose. */
    (*cinfo->err->output_message) (cinfo);
  
    /* Return control to the setjmp point */
    longjmp(myerr->setjmp_buffer, 1);
  }
  
  GLOBAL(int)
  read_JPEG_file (char * filename,unsigned char **image_buf,int *width,int *height)
  {
    /* This struct contains the JPEG decompression parameters and pointers to
     * working space (which is allocated as needed by the JPEG library).
     */
    struct jpeg_decompress_struct cinfo;
    /* We use our private extension JPEG error handler.
     * Note that this struct must live as long as the main JPEG parameter
     * struct, to avoid dangling-pointer problems.
     */
    struct my_error_mgr jerr;
    /* More stuff */
    FILE * infile;		/* source file */
    JSAMPARRAY buffer;		/* Output row buffer */
    int row_stride;		/* physical row width in output buffer */
  
    /* In this example we want to open the input file before doing anything else,
     * so that the setjmp() error recovery below can assume the file is open.
     * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
     * requires it in order to read binary files.
     */
  
    if ((infile = fopen(filename, "rb")) == NULL) {
      fprintf(stderr, "can't open %s\n", filename);
      return 0;
    }
  
    /* Step 1: allocate and initialize JPEG decompression object */
  
    /* We set up the normal JPEG error routines, then override error_exit. */
    cinfo.err = jpeg_std_error(&jerr.pub);
    jerr.pub.error_exit = my_error_exit;
    /* Establish the setjmp return context for my_error_exit to use. */
    if (setjmp(jerr.setjmp_buffer)) {
      /* If we get here, the JPEG code has signaled an error.
       * We need to clean up the JPEG object, close the input file, and return.
       */
      jpeg_destroy_decompress(&cinfo);
      fclose(infile);
      return 0;
    }
    /* Now we can initialize the JPEG decompression object. */
    jpeg_create_decompress(&cinfo);
  
    /* Step 2: specify data source (eg, a file) */
  
    jpeg_stdio_src(&cinfo, infile);
  
    /* Step 3: read file parameters with jpeg_read_header() */
  
    (void) jpeg_read_header(&cinfo, TRUE);
    /* We can ignore the return value from jpeg_read_header since
     *   (a) suspension is not possible with the stdio data source, and
     *   (b) we passed TRUE to reject a tables-only JPEG file as an error.
     * See libjpeg.txt for more info.
     */
  
    /* Step 4: set parameters for decompression */
  
    /* In this example, we don't need to change any of the defaults set by
     * jpeg_read_header(), so we do nothing here.
     */
  
    /* Step 5: Start decompressor */
  
    (void) jpeg_start_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
     * with the stdio data source.
     */
  
    /* We may need to do some setup of our own at this point before reading
     * the data.  After jpeg_start_decompress() we have the correct scaled
     * output image dimensions available, as well as the output colormap
     * if we asked for color quantization.
     * In this example, we need to make an output work buffer of the right size.
     */ 
    /* JSAMPLEs per row in output buffer */
    row_stride = cinfo.output_width * cinfo.output_components;
    /* Make a one-row-high sample array that will go away when done with image */
    buffer = (*cinfo.mem->alloc_sarray)
  		((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
  
    unsigned char *currPtr;
    *width = cinfo.output_width;
    *height = cinfo.output_height;
    (*image_buf) = currPtr = (unsigned char*)malloc(cinfo.output_width*cinfo.output_height*cinfo.output_components*sizeof(unsigned char));
  //   fprintf(stdout,"Read image: (%d,%d,%d)\n",cinfo.output_width,cinfo.output_height,cinfo.output_components);
  //   fflush(stdout);
  
    /* Step 6: while (scan lines remain to be read) */
    /*           jpeg_read_scanlines(...); */
  
    /* Here we use the library's state variable cinfo.output_scanline as the
     * loop counter, so that we don't have to keep track ourselves.
     */
    while (cinfo.output_scanline < cinfo.output_height) {
      /* jpeg_read_scanlines expects an array of pointers to scanlines.
       * Here the array is only one element long, but you could ask for
       * more than one scanline at a time if that's more convenient.
       */
      (void) jpeg_read_scanlines(&cinfo, buffer, 1);
      /* Assume put_scanline_someplace wants a pointer and sample count. */
      currPtr = put_scanline_someplace(currPtr,buffer[0],row_stride);
    }
  
    /* Step 7: Finish decompression */
  
    (void) jpeg_finish_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
     * with the stdio data source.
     */
  
    /* Step 8: Release JPEG decompression object */
  
    /* This is an important step since it will release a good deal of memory. */
    jpeg_destroy_decompress(&cinfo);
  
    /* After finish_decompress, we can close the input file.
     * Here we postpone it until after no more JPEG errors are possible,
     * so as to simplify the setjmp error logic above.  (Actually, I don't
     * think that jpeg_destroy can do an error exit, but why assume anything...)
     */
    fclose(infile);
  
    /* At this point you may want to check to see whether any corrupt-data
     * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
     */
  
    /* And we're done! */
    return 1;
  }
  
  
  void write_JPEG_file (char * filename, int quality, JSAMPLE *image_buffer, int image_width, int image_height) {
    /* This struct contains the JPEG compression parameters and pointers to
     * working space (which is allocated as needed by the JPEG library).
     * It is possible to have several such structures, representing multiple
     * compression/decompression processes, in existence at once.  We refer
     * to any one struct (and its associated working data) as a "JPEG object".
     */
    struct jpeg_compress_struct cinfo;
    /* This struct represents a JPEG error handler.  It is declared separately
     * because applications often want to supply a specialized error handler
     * (see the second half of this file for an example).  But here we just
     * take the easy way out and use the standard error handler, which will
     * print a message on stderr and call exit() if compression fails.
     * Note that this struct must live as long as the main JPEG parameter
     * struct, to avoid dangling-pointer problems.
     */
    struct jpeg_error_mgr jerr;
    /* More stuff */
    FILE * outfile;		/* target file */
    JSAMPROW row_pointer[1];	/* pointer to JSAMPLE row[s] */
    int row_stride;		/* physical row width in image buffer */
  
    /* Step 1: allocate and initialize JPEG compression object */
  
    /* We have to set up the error handler first, in case the initialization
     * step fails.  (Unlikely, but it could happen if you are out of memory.)
     * This routine fills in the contents of struct jerr, and returns jerr's
     * address which we place into the link field in cinfo.
     */
    cinfo.err = jpeg_std_error(&jerr);
    /* Now we can initialize the JPEG compression object. */
    jpeg_create_compress(&cinfo);
  
    /* Step 2: specify data destination (eg, a file) */
    /* Note: steps 2 and 3 can be done in either order. */
  
    /* Here we use the library-supplied code to send compressed data to a
     * stdio stream.  You can also write your own code to do something else.
     * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
     * requires it in order to write binary files.
     */
    if ((outfile = fopen(filename, "wb")) == NULL) {
      fprintf(stderr, "can't open %s\n", filename);
      exit(1);
    }
    jpeg_stdio_dest(&cinfo, outfile);
  
    /* Step 3: set parameters for compression */
  
    /* First we supply a description of the input image.
     * Four fields of the cinfo struct must be filled in:
     */
    cinfo.image_width = image_width; 	/* image width and height, in pixels */
    cinfo.image_height = image_height;
    cinfo.input_components = 3;		/* # of color components per pixel */
    cinfo.in_color_space = JCS_RGB; 	/* colorspace of input image */
    /* Now use the library's routine to set default compression parameters.
     * (You must set at least cinfo.in_color_space before calling this,
     * since the defaults depend on the source color space.)
     */
    jpeg_set_defaults(&cinfo);
    /* Now you can set any non-default parameters you wish to.
     * Here we just illustrate the use of quality (quantization table) scaling:
     */
    jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */);
  
    /* Step 4: Start compressor */
  
    /* TRUE ensures that we will write a complete interchange-JPEG file.
     * Pass TRUE unless you are very sure of what you're doing.
     */
    jpeg_start_compress(&cinfo, TRUE);
  
    /* Step 5: while (scan lines remain to be written) */
    /*           jpeg_write_scanlines(...); */
  
    /* Here we use the library's state variable cinfo.next_scanline as the
     * loop counter, so that we don't have to keep track ourselves.
     * To keep things simple, we pass one scanline per call; you can pass
     * more if you wish, though.
     */
    row_stride = image_width * 3;	/* JSAMPLEs per row in image_buffer */
  
    while (cinfo.next_scanline < cinfo.image_height) {
      /* jpeg_write_scanlines expects an array of pointers to scanlines.
       * Here the array is only one element long, but you could pass
       * more than one scanline at a time if that's more convenient.
       */
      row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride];
      (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }
  
    /* Step 6: Finish compression */
  
    jpeg_finish_compress(&cinfo);
    /* After finish_compress, we can close the output file. */
    fclose(outfile);
  
    /* Step 7: release JPEG compression object */
  
    /* This is an important step since it will release a good deal of memory. */
    jpeg_destroy_compress(&cinfo);
  }
  